Smoke Transport Research Articles

Organic molecular tracers in atmospheric PM1 at urban intensive traffic and background sites in two high-insolation European cities

Atmospheric PM1 has an impact on health and the environment, and is highly variable. PM1 filter samples were collected in urban roof and street sites in two Mediterranean cities in Europe (Barcelona and Madrid) to study the spatial and temporal trends of primary and secondary organic tracer compounds. Both cities are exposed to modern urban emission sources with intensive traffic in their centers. Moreover, their geographical situation in the Mediterranean region favors photo-chemical reactions and accumulation of secondary aerosols, due to sunny anti-cyclonic weather conditions. Barcelona is located along the coast with high relative humidity and an active sea-mountain breeze system, while the relative humidity in Madrid is low in summer, due to its location in the center of the Iberian Peninsula. These differences may influence the accumulation of primary air pollutants and the formation of secondary aerosols. In street site samples, the levels of primary organics, such as polycyclic aromatic hydrocarbons, hopanes and nicotine, were about two times higher than those collected simultaneously at roof sites. Primary emitted levoglucosan and isomers from biomass burning were observed in higher concentrations in winter in both urban areas, but without significant difference between the road and roof sites samples, indicating regional transport of biomass smoke to the cities. Similar roof and street site sample concentrations were also observed for secondary organic aerosol (SOA) compounds, i.e. dicarboxylic acids and oxidation products of isoprene and α-pinene. The SOA compound concentrations were ten times higher in summer compared to winter samples, emphasizing the importance of SOA formation processes in summer. More evidence was obtained that linked the presence of cis-pinonic acid in the filter samples to new particle formation during nucleation. The urban organic PM1 is dominated by SOA, while the primary organic aerosol (POA) tracer compounds from combustion sources, including traffic and biomass burning, dominates in winter.

Role of the Madden‐Julian Oscillation in the Transport of Smoke From Sumatra to the Malay Peninsula During Severe Non‐El Niño Haze Events

AbstractIn June 2013, the Malay Peninsula experienced severe smoke pollution, with daily surface particulate matter (PM) concentrations in Singapore greater than 350 μg/m3, over 2 times the air quality standard for daily mean PM10 set by the U.S. Environmental Protection Agency. Unlike most haze episodes in the Malay Peninsula in recent decades (e.g., the September 2015 event), the June 2013 haze occurred in the absence of an El Niño, during negative Indian Ocean Dipole conditions, with smoke carried eastward to the Peninsula from fires in the Riau province of central Sumatra. We show that June 2013 was not an exceptional event; inspection of visibility data during 2005–2015 reveals two other severe haze events in the Malay Peninsula (August 2005 and October 2010) occurring under similar conditions. Common to all three events was a combination of anomalously strong westerly winds over Riau province concurrent with late phases of the Real‐Time Multivariate Madden‐Julian Oscillation Index, during negative phases of the Indian Ocean Dipole. Our work suggests that identifying the meteorological mechanism driving these westerly wind anomalies could help stakeholders prepare for future non‐El Niño haze events in Singapore and the Malay Peninsula.

Intra-continental wildfire smoke transport and impact on local air quality observed by ground-based and satellite remote sensing in New York City

The wildfires in Fort McMurray of Alberta, Canada, injected large amounts of smoke aerosols in May 2016 and were identified as being one of Canada's major weather events of the year. This paper presents a synergistic remote sensing and in-situ measurement of the resultant smoke plume transport, optical properties, and its impacts on local air quality in New York City (NYC). Comparisons with the operational air quality model forecast (the NOAA National Air Quality Forecasting Capability, NAQFC) performance are presented. The aloft plume intrusions on May 9–13 and 25–29, 2016, and their mixing down into the planetary-boundary layer (PBL) were observed by a combined lidar, ceilometer and other measurement. A decrease in single-scattering albedo and absorption Angstrom exponent near one indicates that the plumes were absorbing aerosol dominated. Dramatic impacts of smoke transport on the ground air quality are demonstrated with a coincident increase of ground PM2.5 (from 5- to 25–30 μg/m3) in NYC urban and upwind rural area, enhancement of the PM2.5 speciation (organic carbon, elemental carbon, potassium ion (K+)) and the ozone exceedance of NAAQS. Using the satellite and model product, we show regional spatial distribution of smoke, multiple transport paths and wildfire sources. Finally, with the lidar vertical profiling observations, we evaluate the model PBL-height (PBLH) and PM2.5 during May 24th to 30th, 2016. The model PBLH shows consistent diurnal variation with the observed mixing layer height (MLH), but is clearly overestimated during the convective daytime hours. On the other hand, when estimating the MLH directly from the model PM2.5 profile, better agreement with observation was indicated. This helps explain the good agreement between the model PM2.5 and surface measurements except for the model overestimate during the morning of May 25 and 26, 2016.

Using TES retrievals to investigate PAN in North American biomass burning plumes

Abstract. Peroxyacyl nitrate (PAN) is a critical atmospheric reservoir for nitrogen oxide radicals, and plays a lead role in their redistribution in the troposphere. We analyze new Tropospheric Emission Spectrometer (TES) PAN observations over North America from July 2006 to July 2009. Using aircraft observations from the Colorado Front Range, we demonstrate that TES can be sensitive to elevated PAN in the boundary layer (∼ 750 hPa) even in the presence of clouds. In situ observations have shown that wildfire emissions can rapidly produce PAN, and PAN decomposition is an important component of ozone production in smoke plumes. We identify smoke-impacted TES PAN retrievals by co-location with NOAA Hazard Mapping System (HMS) smoke plumes. Depending on the year, 15–32 % of cases where elevated PAN is identified in TES observations (retrievals with degrees of freedom (DOF) > 0.6) overlap smoke plumes during July. Of all the retrievals attempted in the July 2006 to July 2009 study period, 18 % is associated with smoke . A case study of smoke transport in July 2007 illustrates that PAN enhancements associated with HMS smoke plumes can be connected to fire complexes, providing evidence that TES is sufficiently sensitive to measure elevated PAN several days downwind of major fires. Using a subset of retrievals with TES 510 hPa carbon monoxide (CO) > 150 ppbv, and multiple estimates of background PAN, we calculate enhancement ratios for tropospheric average PAN relative to CO in smoke-impacted retrievals. Most of the TES-based enhancement ratios fall within the range calculated from in situ measurements.

A mathematical model for heat detector activation time under ship fire in a long-narrow space

The prediction of fire detector activation time is essential to ship fire safety design. In this study, a model was developed to predict heat detector activation time under ship fires in a long-narrow space. Firstly, smoke transport time of fires in a long-narrow space was determined by the time of smoke spreading from fire resource to the target location (i.e. the location of heat detector in this study) on the ceiling. Theoretical calculation method concerning smoke transport time under steady fires was then proposed based on the correlations of temperature and velocity developed in previous studies. Series of experiments were conducted in a reduced-scale test rig for validation. Using the proposed method, a dimensionless model of transport time under steady fires was theoretically derived. Secondly, following the temperature rise equation of heat detector and considering the influence of smoke transport time lag, analytic solution was obtained by integrating for steady or quasi-steady fires. And a time-varying spreadsheet template combining with Improved Euler's Method was proposed to predict the activation time for unsteady fires. Case study results showed the proposed model is applicable for long-narrow spaces, which breaks its usage limits of DETACT-T2.

3D printed scaled setup for smoke transport analysis in a subterranean passenger platform

In this work, the study of smoke fire transportation inside of a subway passenger platform is presented. The study includes a set of numerical simulations to observe the behavior of the smoke inside the platform. Two smoke transport simulations using the FDS program are also included. Subsequently, the development of a 3D - 1:100 scale model is described and it was used to perform an experimental observation of the phenomenon. The model was built by using a 3D printer which allowed to include more architectural details of the real scenario. The inclusion of these details allowed to observe qualitative similarity between the results of the simulation and the experimental work. Although there are clear differences between what could happen in a real scenario and what was observed in the scale model, it was identified that the model is an important complement to the simulations. In addition to the simulations, the use of this type of 3D models allows the observation of the phenomenon by different specialists such as firefighters, policeman, medical personnel, etc., in the same place and its intention is to provide a more interactive tool to the observation group, increasing the time devoted to the development of contingency actions and reducing the costs associated with the logistics of a real simulacrum. The model allows to better identify the strengths, opportunities, weaknesses and threats of the contingency procedures developed by the safety and hygiene groups and to make their corresponding adjustments if necessary.

A study on the maximum temperature of ceiling jet induced by rectangular-source fires in a tunnel using ceiling smoke extraction

This study analyzes the physics characteristics of the flame plume temperature, induced by a ceiling jet and their coupling with an extraction flow. As it is knows, the maximum increase in the temperature of a ceiling jet is a key parameter for tunnel fire safety. The ceiling maximum temperature has been analyzed and its evolution model has also been correlated in the past. However, those previous suggested correlations had considered the fire source shape is square or circular. Actually the van shape is rectangular, the corresponding fire source may be rectangular, which is necessary to extend it to other conditions of rectangular fire sources. It has also been noted that the smoke transport characteristics changed by the ceiling smoke extraction. The aim of this experimental work is to study the maximum increase in the temperature of a ceiling jet induced by rectangular-source fires with different burner aspect ratios (ranging from 1 to 8.2) in a tunnel, using a ceiling smoke extraction. The effects of different burner aspect ratios on the ceiling maximum smoke temperature increase were studied with and without a ceiling smoke extraction. The change of the burner aspect ratios, the ceiling mechanical extraction rate, and the heat release rate were also analyzed. The evolution characteristics of the ceiling maximum plume temperature rise, considering the different burner aspect ratios, with the change in the aspect ratios of burners without the ceiling extraction were firstly obtained. A new normalized equation of the ceiling maximum plume temperature, through the addition of an impact factor for the ceiling smoke extraction rate, of a ceiling jet induced by rectangular-source fires was established. The results indicated that the new global model can effectively predict experimental data.

Wildfire smoke transport and impact on air quality observed by a mullti-wavelength elastic-raman lidar and ceilometer in New York city

The intense wildfires from the western Canada in May 2016 injected large amount of smoke into the atmosphere. This paper presents integrated observation of the event by a lidar, ceilometer, and satellite together with models and an assessment of smoke plume impacts on local air quality in New York City (NYC) area. A dense aloft plume on May 20 and a boundary layer plume on May 25 are analyzed. The smoke mixing into planetary-boundary-layer (PBL) and strong diurnal variation of PBL-top are shown. For the 2ndcase, the ground PM2.5 measurements show a significant increase in both the urban and upwind non-urban areas of NYC. The smoke sources and transport paths are further verified by the satellite observations and HYSPLIT model data.

Comparing the height and area of wild and prescribed fire particle plumes in south-east Australia using weather radar

Smoke pollution from landscape fires is a major health issue. Prescribed burning aims to reduce the area and impact of wildfire, but itself produces smoke pollution. This raises the question as to whether the smoke production and transport from prescribed fires is substantially different compared to wildfires. We examined the maximum height, width and areal footprint of large-particle plumes from 97 wild and 126 prescribed fires in south-eastern Australia using the existing network of weather radars. Radar detects large particles in smoke (probably those >100 μm) and hence is an imperfect proxy for microfine (<2 μm) particles that are known to affect human health. Of the 223 landscape fires, ~45% of plumes were detected, with the probability being >0.8 for large fires (>100 000 ha) regardless of type, closer than 50 km from the radar. Plume height was strongly influenced by fire area, the height of the planetary boundary layer and fire type. Plume heights differed between wildfire (range 1016–12 206 m, median 3260 m) and prescribed fires (range 706–6397 m, median 1669 m), and prescribed fires were predicted to be 800–1200 m lower than wildfires, controlling for other factors. For both wildfires and prescribed fires, the maximum plume footprint was always near the ground.

Effects of ambient pressure on transport characteristics of thermal-driven smoke flow in a tunnel

Thermal-driven smoke flow is the greatest threat to the trapped people in tunnels, and the basic understanding of the smoke transport characteristics is necessary for the engineering applications of smoke control and exhausting system. However, most of the previous studies only focused on the smoke transport at normal pressure. As a matter of fact, the ambient pressure decreases with the increasing of the altitude, and the influence of different ambient pressures on the transport characteristics of thermal-driven smoke has been rarely considered before. This paper presents an investigation on the effect of ambient pressure on the smoke transport characteristics in a tunnel. A series of fire simulations were conducted in a full scale road tunnel with ambient pressure ranged from 100 kPa to 50 kPa and the heat release rate (HRR) varied from 3 MW to 15 MW. The smoke mass transport along the tunnel for different conditions is analyzed, and results show that for a certain HRR, the smoke mass flow rate decreases with reduced ambient pressure due to the decreased air density and the weakening of air entrainment strength. Based on the dimensional analysis, a quantitative model to predict the average smoke mass flow rate in the tunnel is proposed considering both ambient pressure and HRR. Moreover, the credibility of the predictive model is validated by comparing with a wide range of experimental results from both full scale and reduced scale experiments at different pressures.

Creating Aerosol Types from CHemistry (CATCH): A New Algorithm to Extend the Link Between Remote Sensing and Models

AbstractCurrent remote sensing methods can identify aerosol types within an atmospheric column, presenting an opportunity to incrementally bridge the gap between remote sensing and models. Here a new algorithm was designed for Creating Aerosol Types from CHemistry (CATCH). CATCH‐derived aerosol types—dusty mix, maritime, urban, smoke, and fresh smoke—are based on first‐generation airborne High Spectral Resolution Lidar (HSRL‐1) retrievals during the Ship‐Aircraft Bio‐Optical Research (SABOR) campaign, July/August 2014. CATCH is designed to derive aerosol types from model output of chemical composition. CATCH‐derived aerosol types are determined by multivariate clustering of model‐calculated variables that have been trained using retrievals of aerosol types from HSRL‐1. CATCH‐derived aerosol types (with the exception of smoke) compare well with HSRL‐1 retrievals during SABOR with an average difference in aerosol optical depth (AOD) <0.03. Data analysis shows that episodic free tropospheric transport of smoke is underpredicted by the Goddard Earth Observing System‐ with Chemistry (GEOS‐Chem) model. Spatial distributions of CATCH‐derived aerosol types for the North American model domain during July/August 2014 show that aerosol type‐specific AOD values occurred over representative locations: urban over areas with large population, maritime over oceans, smoke, and fresh smoke over typical biomass burning regions. This study demonstrates that model‐generated information on aerosol chemical composition can be translated into aerosol types analogous to those retrieved from remote sensing methods. In the future, spaceborne HSRL‐1 and CATCH can be used to gain insight into chemical composition of aerosol types, reducing uncertainties in estimates of aerosol radiative forcing.

The influence of continental air masses on the aerosols and nutrients deposition over the western North Pacific

The air masses transported from East Asia have a strong impact on the aerosol properties and deposition in the marine boundary layer of the western North Pacific (WNP) during winter and spring. We joined a cruise between 17 Mar. and 22 Apr. 2014 and investigated the changes of aerosol composition and size distribution over the remote WNP and marginal seas. Although the secondary aerosol species (SO42−, NO3− and NH4+) in remote WNP were influenced significantly by the continental transport, NH4+ concentrations were lower than 2.7 μg m−3 in most sampling days and not correlated with non-sea-salt (nss)-SO42- suggesting that the ocean could be a primary source of NH4+. Moderate Cl− depletion (23%) was observed in remote WNP, and the inverse relationship between Cl− depletion percentages and nss-K+ in aerosols suggested that the transport of biomass burning smoke from East Asia might be a vital extra source of Cl−. Both Asian dust and haze events were encountered during the cruise. Asian dust carried large amounts of crustal elements such as Al and Ti to the WNP, and the dusty Fe deposition may double its background concentration in seawater. Differently, a dramatic increase of dry deposition flux of dissolved particulate inorganic nitrogen was observed during the haze event. Our study reveals that the transport of different continental air masses may have distinct biogeochemical impacts on the WNP by increasing the fluxes of different nutrient elements and potentially changing the nutrient stoichiometry.

Simulation of Optical Properties and Direct and Indirect Radiative Effects of Smoke Aerosols Over Marine Stratocumulus Clouds During Summer 2008 in California With the Regional Climate Model RegCM

AbstractThe regional climate model RegCM has been modified to better account for the climatic effects of biomass‐burning particles. Smoke aerosols are represented by new tracers with consistent radiative and hygroscopic properties to simulate the direct radiative forcing (DRF), and a new parameterization has been integrated for relating the droplet number concentration to the aerosol concentration for marine stratocumulus clouds (Sc). RegCM has been tested during the summer of 2008 over California, when extreme concentration of smoke, together with the presence of Sc, is observed. This work indicates that significant aerosol optical depth (AOD) (~1–2 at 550 nm) is related to the intense 2008 fires. Compared to Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer, the regional pattern of RegCM AOD is well represented although the magnitude is lower than satellite observations. Comparisons with Polarization and Directionality of Earth Reflectances (POLDER) above‐clouds aerosol optical depth (ACAOD) show the ability of RegCM to simulate realistic ACAOD during the transport of smoke above the Pacific Ocean. The simulated single scattering albedo is ~0.90 (at 550 nm) near biomass‐burning sources, consistent with OMI and POLDER, and smoke leads to shortwave heating rates ~1.5–2°K d−1. RegCM is not able to correctly resolve the daily patterns in cloud properties notably due to its coarse horizontal resolutions. However, the changes in the sign of the DRF at top of atmosphere (TOA) (negative to positive) from clear‐sky to all‐sky conditions is well simulated. Finally, the “aerosol‐cloud” parameterization allows simulating an increase of the cloud optical depth for significant concentrations, leading to large perturbations of radiative fluxes at TOA.

Dimensionless analytical solutions for steady-state fire smoke spread through high-rise shaft

Analytical solutions in terms of dimensionless numbers for the smoke spread through high-rise shafts during fires are essential to provide a fundamental understanding of smoke transport physics, which is a complex coupled heat and mass transfer problem. Existing solutions are often dimensional based on simplification of the problem such as assuming adiabatic conditions. In order to obtain the dimensionless analytical solutions, energy balance equation, mechanical energy equation and mass balance equation were established for smoke spread in high-rise buildings under both mechanical and natural venting conditions. Experiments were designed and conducted on two scaled shafts with different sizes and materials, and the measured results were compared to the dimensionless analytical solutions. It was found that the dimensionless analytical solutions could predict temperature profiles, mass flow rate and neutral plane level accurately. The effect of the adiabatic assumption on the accuracy was also discussed. For example, due to the adiabatic assumption, the error of the calculated mass flow rate required during mechanical venting to maintain a high-rise shaft smoke free was found to increase with a dimensionless number, ω, defined by the geometrical and thermal properties of the shaft.

Multi year aerosol characterization in the tropical Andes and in adjacent Amazonia using AERONET measurements

This work focuses on the analysis of columnar aerosol properties in the complex geophysical tropical region of South America within 10–20° South and 50–70° West. The region is quite varied and encompasses a significant part of Amazonia (lowlands) as well as high mountains in the Andes (highlands,∼4000 m a.s.l.). Several AERONET stations were included to study the aerosol optical characteristics of the lowlands (Rio Branco, Ji Parana and Cuiaba in Brazil and Santa Cruz in Bolivia) and the highlands (La Paz, Bolivia) during the 2000–2014 period. Biomass-burning is by far the most important source of aerosol in the lowlands, particularly during the dry season (August–October). Multi-annual variability was investigated and showed very strong burning activity in 2005, 2006, 2007 and 2010. This resulted in smoke characterized by correspondingly strong, above-average AODs (aerosol optical depths) and homogeneous single scattering albedo (SSA) across all the stations (∼0.93). For other years, however, SSA differences arise between the northern stations (Rio Branco and Ji Parana) with SSAs of ∼0.95 and the southern stations (Cuiaba and Santa Cruz) with lower SSAs of ∼0.85. Such differences are explained by the different types of vegetation burned in the two different regions. In the highlands, however, the transport of biomass burning smoke is found to be sporadic in nature. This sporadicity results in highly variable indicators of aerosol load and type (Angstrom exponent and fine mode fraction) with moderately significant increases in both. Regional dust and local pollution are the background aerosol in this highland region, whose elevation places it close to the free troposphere. Transported smoke particles were generally found to be more optical absorbing than in the lowlands: the hypothesis to explain this is the significantly higher amount of water vapor in Amazonia relative to the high mountain areas. The air-mass transport to La Paz was investigated using the HYSPLIT air-concentration five-days back trajectories. Two different patterns were clearly differentiated: westerly winds from the Pacific that clean the atmosphere and easterly winds favoring the transport of particles from Amazonia.

Mesoscale modeling of smoke transport from equatorial Southeast Asian Maritime Continent to the Philippines: First comparison of ensemble analysis with in situ observations

AbstractAtmospheric transport of smoke from equatorial Southeast Asian Maritime Continent (Indonesia, Singapore, and Malaysia) to the Philippines was recently verified by the first‐ever measurement of aerosol composition in the region of the Sulu Sea from a research vessel named Vasco. However, numerical modeling of such transport can have large uncertainties due to the lack of observations for parameterization schemes and for describing fire emission and meteorology in this region. These uncertainties are analyzed here, for the first time, with an ensemble of 24 Weather Research and Forecasting model with Chemistry (WRF‐Chem) simulations. The ensemble reproduces the time series of observed surface nonsea‐salt PM2.5 concentrations observed from the Vasco vessel during 17–30 September 2011 and overall agrees with satellite (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and Moderate Resolution Imaging Spectroradiometer (MODIS)) and Aerosol Robotic Network (AERONET) data. The difference of meteorology between National Centers for Environmental Prediction (NCEP's) Final (FNL) and European Center for Medium range Weather Forecasting (ECMWF's) ERA renders the biggest spread in the ensemble (up to 20 μg m−3 or 200% in surface PM2.5), with FNL showing systematically superior results. The second biggest uncertainty is from fire emissions; the 2 day maximum Fire Locating and Modelling of Burning Emissions (FLAMBE) emission is superior than the instantaneous one. While Grell‐Devenyi (G3) and Betts‐Miller‐Janjić cumulus schemes only produce a difference of 3 μg m−3 of surface PM2.5 over the Sulu Sea, the ensemble mean agrees best with Climate Prediction Center (CPC) MORPHing (CMORPH)'s spatial distribution of precipitation. Simulation with FNL‐G3, 2 day maximum FLAMBE, and 800 m injection height outperforms other ensemble members. Finally, the global transport model (Navy Aerosol Analysis and Prediction System (NAAPS)) outperforms all WRF‐Chem simulations in describing smoke transport on 20 September 2011, suggesting the challenges to model tropical meteorology at mesoscale and finer scale.

An Alternative Method for Thermal Plume–Induced Aerosol Release and Deposition Calculations in Large Geometries Using fireFoam

Being a particle physics laboratory, the European Organization for Nuclear Research (CERN) plans, constructs, and maintains installations emitting ionizing radiation during operation. Activation of present material is a consequence. Hence, fire scenarios for certain CERN installations must take into account the presence of radioactive material. Releases of gaseous, liquid, or solid combustion products, e.g., attached to aerosols, are taken so far into account by a worst case approach. Scenarios taking place in underground installations assume hence a smoke transport coefficient of 100% of release toward the surface level, independent of the local geometry. For a radioactive inventory identified in a certain fire load, this results in a conservative release.To overcome this conservative worst case approach, a computational fluid dynamics model based on FM Global’s fireFoam 2.2.x is proposed. Its Lagrangian library was modified in order to provide aerosol release and deposition information based on more detailed interaction data between Lagrangian particles and their surrounding geometry. Results are shown for a CERN-typical large-scale experimental cavern placed 100 m below surface level. A simple diffusion burner is modeled inside the cavern to create a thermal plume emerging from a 1.5-MW fire over 14 min. Lagrangian particles are used to model aerosols with an aerodynamic diameter of 1, 10, and 100 μm, injected into the emerging thermal plume. Results for particle release and deposition vary according to aerodynamic diameter. In the present case, maximums of ~32% and 39% are found for 1- and 10-μm particles, respectively, being released to the surface level.

An agricultural biomass burning episode in eastern China: Transport, optical properties, and impacts on regional air quality

AbstractAgricultural biomass burning (ABB) has been of particular concern due to its influence on air quality and atmospheric radiation, as it produces large amounts of gaseous and aerosol emissions. This paper presents an integrated observation of a significant ABB episode in Nanjing, China, during early June 2011, using combined ground‐based and satellite sensors (Moderate Resolution Imaging Spectroradiometer, Atmospheric Infrared Sounder, Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and Ozone Monitoring Instrument products). The time‐height distribution, optical properties, sources and transport of smoke, and its impacts on air quality are investigated. Lidar profiles indicate that the smoke aerosols are confined to the planetary boundary layer (PBL) and have a depolarization ratio of less than 0.08. The aerosol optical depths increase from 0.5 to 3.0 at 500 nm, while the extinction‐related Angstrom exponent increases from 1.1 to 1.6 at the wavelength pair of 440–870 nm. The single‐scattering albedo becomes lower at 670–1020 nm following the ABB intrusion and particularly shows a decreasing tendency between wavelengths of 440 to 1020 nm. The absorption Angstrom exponent (0.7) is smaller than 1.0, which may indicate the aged smoke particles mixed or coated with the urban aerosols. Surface particular matter PM10 and PM2.5 show a dramatic increase, reaching hourly mean of 800 µg/m3 and 485 µg/m3, respectively, which results in a heavy air pollution event. The stagnant and high‐moisture weather provides favorable conditions for the aerosols to accumulate near the surface. Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) also illustrate that the large‐scale aerosols are primarily present in the PBL and transported to the ocean, but some dense smoke plumes are misclassified as cloud or polluted dust. By comparing with the observations, we found that the Weather Research and Forecasting–Chemistry model captured the accumulation and downwind transport of surface PM2.5 from 20:00 on 2 June to 10:00 on 3 June (phase 1) but showed a dramatic underestimate from 20:00 on 3–4 June (phase 2) when dense aerosols are present. Such a discrepancy in the model is associated with the improper vertical apportion of transported smoke and atmospheric diffusion conditions when comparing with the observed aerosol and wind profiles. In addition, the model simulations indicate that the transported smoke can contribute to 50–70% of the ground‐level PM2.5 in Nanjing.

The link between smoke blanketing of European Russia in summer 2016, Siberian wildfires and anomalies of large-scale atmospheric circulation

Analysis of smoke blanketing of European Russia (ER) in summer 2016 is presented. The results of the analysis indicate that the cause of the smoky atmosphere over ER was long-range transport of smoke from wildfires in Siberia. The aerosol optical thickness at a wavelength of 550 nm over ER in late July reached 3. The features of circulation in the troposphere over northern Eurasia in July 2016, with an anomalous east transfer of combustion products in the troposphere over thousands of kilometers, which is opposite to the westerly transfer prevailing in the mid-latitudes, are discussed. A comparison of variations in the probability distribution functions of the aerosol optical thickness is performed for ER and Siberia for the summer periods in different years with massive wildfires.

Downward solar global irradiance at the surface in São Paulo city—The climatological effects of aerosol and clouds

AbstractWe analyzed the variability of downward solar irradiance reaching the surface at São Paulo city, Brazil, and estimated the climatological aerosol and cloud radiative effects. Eleven years of irradiance were analyzed, from 2005 to 2015. To distinguish the aerosol from the cloud effect, the radiative transfer code LibRadtran was used to calculate downward solar irradiance. Two runs were performed, one considering only ozone and water vapor daily variability, with AOD set to zero and the second allowing the three variables to change, according to mean climatological values. The difference of the 24 h mean irradiance calculated with and without aerosol resulted in the shortwave aerosol direct radiative effect, while the difference between the measured and calculated, including the aerosol, represented the cloud effect. Results showed that, climatologically, clouds can be 4 times more effective than aerosols. The cloud shortwave radiative effect presented a maximum reduction of about −170 W m−2 in January and a minimum in July, of −37 W m−2. The aerosol direct radiative effect was maximum in spring, when the transport of smoke from the Amazon and central parts of South America is frequent toward São Paulo. Around mid‐September, the 24 h radiative effect due to aerosol only was estimated to be −50 W m−2. Throughout the rest of the year, the mean aerosol effect was around −20 W m−2 and was attributed to local urban sources. The effect of the cloud fraction on the cloud modification factor, defined as the ratio of all‐sky irradiation to cloudless sky irradiation, showed dependence on the cloud height. Low clouds presented the highest impact while the presence of high clouds only almost did not affect solar transmittance, even in overcast conditions.